WKColorButton leaks a UIColor.

Found by clang static analyzer:

'WKColorButton' lacks a 'dealloc' instance method but must release '_color'

--

#pragma mark - WKColorButton

@interface WKColorButton : UIButton
@property (nonatomic, strong) UIColor *color;

+ (instancetype)colorButtonWithColor:(UIColor *)color;
@end

@implementation WKColorButton

+ (instancetype)colorButtonWithColor:(UIColor *)color
{
    WKColorButton *colorButton = [WKColorButton buttonWithType:UIButtonTypeCustom];
    colorButton.color = color;
    colorButton.backgroundColor = color;
    return colorButton;
}

@end